1. Field of the Invention
The present invention relates to an inflator for generating a gas that is supplied to an airbag disposed in an automobile as a safety device.
2. Related Technology
An airbag device is constituted by an inflator serving as a gas generating device and an airbag, and protects an occupant from an impact generated during a collision by deploying the airbag using gas generated by the inflator.
FIG. 6 is a sectional view illustrating a structure of a dual stage type inflator 1. In the inflator 1, a pressure vessel 2 constituted by a diffuser 2a and a base 2b accommodates an igniter 3 that is activated by an electric signal generated when a collision is detected and a gas generating agent 4 that is ignited by the igniter 3 to generate a large amount of gas instantaneously.
During the collision, the generated gas is discharged from a gas discharge hole 2aa provided in the diffuser 2a and introduced into an airbag, whereby the airbag is deployed. However, the gas contains a large amount of solid residue, and therefore, in order to protect the health of the occupants and the airbag, the solid residue is collected by passing the gas through a filter 5, and the gas is cooled.    Patent Document 1: Japanese Patent Application Publication H9-76869
A reference numeral 6 in FIG. 6 denotes an ignition charge that amplifies and transfers an ignition energy of the igniter 3 instantaneously in order to burn the gas generating agent 4. Further, 7 denotes an inner cover for preventing the gas generating agent 4 from spilling out when the diffuser 2a is welded to the base 2b and preventing the gas from leaking out from an upper end of the filter 5 when the inflator 1 is activated.
Incidentally, wire wound filters have recently come into use as the filter 5. As shown in FIG. 7, a wire wound filter is formed by winding metal wire 5a diagonally into a cylindrical shape and then fixing the metal wire 5a in the cylindrical shape by sintering. A wire wound filter basically has the structure of a spring and therefore deforms extremely easily in a height direction.
Hence, when the wire wound filter is press-fitted into the base of the pressure vessel, the metal wire is likely to rise up and accumulate directly behind a part that has entered the base, thereby generating a large frictional force. To counter this frictional force, therefore, a large press-fitting force is required.
However, when a large press-fitting force is applied, the filter deforms greatly in the height direction, and as a result, a permeability of the filter may be adversely affected such that the inflator is not activated correctly. Therefore, when a wire wound filter is employed, the press-fitting characteristic into the base must be improved.
Using a test device 7 shown in FIG. 8, in which a test sample 12 carried on a load cell 11a is pressed by a hand press 11b, deformation of three identical wire wound filters C, D, E was measured. Measurement results are shown in FIG. 9.
It is evident from FIG. 9 that when the pressure exerted on the wire wound filter exceeds 1097 N, the wire wound filter starts to deform greatly. Therefore, when press-fitting the wire wound filter into the base, the press-fitting pressure must be controlled to or below 1097 N.
Meanwhile, a wire wound filter formed with an outer diameter of 64.26 mm (design value: 64.1±0.25 mm) and a height of 31.02 mm using metal wire having a diameter of 0.36 mm was press-fitted into a base having an inner diameter of 63.72 mm at 1097 N using the test device described above.
It was found as a result that even though the outer diameter of the wire wound filter was within a design dimension tolerance, an inner peripheral portion on an upper side of the paper surface, indicated by a thin arrow in FIG. 10, could not be press-fitted into the base at a pressure of 1097 N. In other words, the filter could not be press-fitted into the base even when sufficient pressure for deforming the filter was applied. Note that a direction indicated by a thick arrow in FIG. 10 is a pressure application direction.